After reading hundreds of threads on the subject of aftermarket audio upgrades and being inspired by the accomplishment of others and appreciating their willingness to share their knowledge and expertise in this field, I felt compelled to embark on a DIY journey even though I had never before installed any aftermarket audio gear in any car, let alone a brand new and beloved 2011 M3 sedan.

The installation...
Fig 1: jtsherri's plastic spacer are cut so precisely, that I used them as gaskets and applied 3/8" wide weatherstripping to the undersides of the Earthquake SWS-8 rims to interface with the spacers which in turn contacted the enclosures directly. This way the OEM 'notch' could be covered and sealed fairly well. I also drilled two holes into the spacer at the notch to snugly fit two protruding 14 AWG speaker wires.

Fig 2: Adopting adc's crossover location, I modified it by installing it at an angle to avoid cutting any foam. There are three points of contact between it and the door panel.

Fig 3: At these specific points, Dynamat Extreme was used underneath the crossover to bind it from below. More Dynamat Extreme was applied over it to firmly secure it from above while keeping the ventilation holes open. Decide on your jumper settings before final mounting!

Fig 4: The Rainbow CAL25 tweeter is only ~2 mm wider in diameter than the OEM tweeter, so it will fit directly into the OEM plastic housing albeit with the housing tabs flared out a bit. Thin Dynamat tape helped to secure the tweeter in place while staying hidden from view.

Fig 5: Cardboard template of the 5.25" SLC 230.25 NG to show that it will fit under the OEM rear deck grills.

Fig 6: The smaller circle represents the actual cutout diameter through which the speaker frame fits. The pushpin kept both templates in coaxial alignment to allow tracing two chalk circles, one for the cutout and the other for the speaker frame. Note that two sections of the perimeter ridge also needed to be cut to accomodate the speaker frame.

Fig 7: A 4.75" hole cutter is the perfect size for the Rainbow SLC 230.25 NG as its cutout diameter happens to be 4.72"

Fig 8: Both sides of the rear deck cut out to accomodate a pair of 5.25" midrange drivers.

Fig 9: I used the leftover cutout material to Dremel out crescent shaped fill-ins to block out the remaining gap from the original off-center 4" midrange hole. Note that the tweeter was installed with an angle mount which had already been spray painted matte black.

Fig 10: The 5.25" driver was bolted on the underside to the plastic installation ring that came with the Rainbow component kit. This greatly reinforced the speaker mounting by stiffening the fiberboard and adding structural rigidity to support the extra weight of the 5.25" speakers. Note that the pink OEM insulation material had to be discarded.

Fig 11: Dynamat Extreme, more useful than duct tape!

Fig 12: Two more Rainbow crossovers fit on the rear deck foam and were Dynamat taped in place. Note that the height of the two crossovers when laying on the foam is just barely lower than the rearmost plastic vent piece.

Fig 13: The rear parcel shelf has been reinstalled demonstrating that both crossovers fit with no deformation of the rear deck. OEM foam above and below the crossovers eliminates any noise or vibration. OEM grills fit right back into place without any problems.

Fig 15: A wooden plank (13.5" x 8.0" x 0.5" birch) was screwed to two perforated metal straps such that the straps could accommodate OEM 8mm bolts (black) at the correct position. Longer M5-80 bolts (silver) fit through drilled holes and were also in the correct position to fit into two OEM mounting holes.

Fig 16: The amplifier platform was bolted in place with OEM bolts (black) and longer M5-80 bolts (silver) at the exact four positions that the OEM amplifier mounting frame had used. This involved a LOT of test fitting as the mounting positions were NOT in symmetric locations.

Fig 17: JL Audio XD700/5 amp connected to Technic's HiFi harness which is connected to the OEM head unit interface + OEM speaker wires. Tremendous time saver, and NO cutting of OEM wires here! The amplifier screws into the wooden plank. I have since organized the 4 AWG wires more cleanly.

Is there anything unsafe that I need to address? Any glaring deficiencies or omissions? Thus far, I'm extremely happy with the new audio quality and have no regrets with this project.

Very nice especially for it being your first install. Do you have more pictures of how you removed the rear deck? A lot of people have asked questions about this but no one has really detailed the removal.

Real quickly,
1. Remove the rear seat cushion bench by pulling the front edge upward to free it from 2 large metal clips.
2. Unclip the plastic covers for the 3 parcel shelf child-restraint latches by pushing in the two rear tabs from each. Remove the single bolt (Torx40) to free each assembly. Release the U-shaped metal retaining tabs from the rear deck.
3. Remove 2 bolts (Torx50) at the base of the empty seat near the center.
4. Remove 3 bolts (Torx50) for each of the 3-point safety belts. Note the secondary alignment screw for reassembly later. Also remove the plastic trim piece at the origin of each belt. Just push the outer corners together since the pieces are C-shaped.
5. From inside the trunk looking up, free 2 latches with a screwdriver oriented upwards utilizing the extreme tip of the 'L'-shaped metal prong as a fulcrum. Lever the abutting shiny steel piece (with the circle cutout) outwards with just the screwdriver tip by pushing against a small notch until you hear the click of the latch releasing the D-ring on the upper seat back. The seat back should now be able to tip forward. The dark 'L'-shaped metal piece NEVER moves. Don't fiddle with any distant white plastic pieces either. But not to worry, if dislodged (which I did to both sides while fumbling around), they can be repositioned back in place via the front of the latch since they will only fit correctly one way.
6. Pull out the 5 plastic retaining plugs along the front edge of the rear deck.
7. Remove the 'AIRBAG' plastic cover plates with a small screwdriver. Remove the screw (Torx20) underneath.
8. Pull the C-pillar trim directly towards the front of the car ~0.5 inch to release 2 metal clips along the rear window edge from their respective slots. The C-pillar can then come right out.
9. The rear parcel shelf should be free to come out with some coaxing. Just push the safety belt clips through their holes since they'll fit through. The 3 U-shaped metal retaining tabs for the upper child-restraint latches were unbolted earlier and may come undone. Just note their location and orientation for reassembly later.

Without question, the trickiest part was disengaging the 'hidden' latches located in the trunk that bind to the tops of the seat backs where the D-rings are situated (Step 5). I spent over an hour trying to figure this mechanism out. During the process I knocked both white plastic pieces out of alignment and mangled the foam. However, as mentioned earlier, the plastic pieces can be put back in A-OK. The key is the fact that the shiny metal part SLIDES outward with respect to the dark metal part...

I used the stock left carpet trim and plastic cover (not the 'taller' one that others have ordered to accommodate stacked amps). The JL Audio XD fits with headroom to spare. No heat issues or power outages thus far (but I don't play music extremely loud either). Ventilation should be no worse than with the OEM amp. I'll have to wait until next summer to see if very hot ambient temperatures have any effect (but I really don't think so).

adc,

I'm no audio expert, but these are my settings:

1. I have the same identical crossovers for the Front Left, Front Right, Rear Left, and Rear Right (even though some components are 4" midranges and some are 5.25"). I also happen to use the same settings at all 4 corners (for no other reason than simplicity and in case the 'pucks' got mixed up, it didn't matter). I originally had...
S1: A (3200 Hz midrange lo-pass)
S2: 3 (tweeter notch on)
S3: 4 (reference soft, 2 dB per octave high frequency drop off)
S4: -8 (tweeter polarity in phase)
S5: +7 (tweeter polarity in phase)

But when I installed a Rainbow SLC 210.25 NG midrange + tweeter component in one door and compared it to the OEM midrange + tweeter in the other door (albeit with the OEM amplifier with its modified signals feeding both front channels), the highs on the Rainbow seemed comparatively soft or muted. Plus, I perceived that I wasn't getting enough sound out of the 4" midrange, so I decided to change and go with...
S1: B (3800 Hz midrange lo-pass)
S2: 2 (tweeter notch off)
S3: 3 (middle optimum tweeter attenuation)
S4: -8 (tweeter polarity in phase)
S5: +7 (tweeter polarity in phase)

The highs are definitely loud now. Perhaps too much, since I have to turn the treble down (and the bass up). A middle of the road setting with...
S1: B
S2: 3
S3: 4
S4: -8
S5: +7
might be a better compromise. Since I've already Dynamat stuck everything in place and reinstalled all the panels, I probably won't be able to realistically adjust them anymore, but I'm certainly happy with the way it currently sounds.

2. For the JL Audio XD700/5, I have all the gain settings (Channels 1/2, 3/4, mono sub) at their lowest. Sounds strange, but when I specifically tried to adjust the input sensitivities with 1000 Hz and 50 Hz sine wave test tones at 0 dB reference levels, my voltmeter (Extech Pocket MultiMeter DM110 from Lowe's) would not register any voltage >1 out of any of the speaker outputs even when dialing up the gain. For 4 Ohm Rainbows, the target voltages were expected to be 17.4V for Channels 1/2 and 3/4. The voltage output for the 2 Ohm Earthquake SWS-8Xs (pair of 4 Ohms in parallel) should have been 26.8V, but again I couldn't get any value. I was probably doing something fundamentally wrong but rather than risk distortion with higher gain sensitivities, I just left them all at their lowest settings (all the way counter-clockwise). When connected, the XD700/5 and all 10 speakers were plenty loud and clear so I quit trying to troubleshoot it and accepted it as is.

As for the amp's crossover filters, I have the front SLC 210.25 NG (4"+1") hi-passed at 95 Hz, the rear SLC 230.25 NG (5.25"+1") hi-passed at 80 Hz, and the SWS-8X (8") lo-passed at 145 Hz. Nothing too scientific here, but it seems to work.

I'm probably in the very small minority, but I actually like hearing the rear channels. I have the fader favoring the rear by a few clicks, and I wanted more midbass from back there. If all I wanted was rear fill, I wouldn't have gone through the trouble of upsizing to 5.25". Rear coaxials would have also been simpler, but I thought to myself, heck, if I'm going to rip this car apart I might as well go full bore. Knowing that the rear deck could come out fully (as others had shown) was the key deciding factor in allowing this project to go forward.

3. I have very simple, basic tools. Ratchets of various sizes, along with metric sockets and torx bits are vitally important. Socket extenders help, too. Tools I actually bought for this project include Bojo trim panel tools, the multimeter, a propane torch (to melt solder to secure 4 AWG wire into the battery distribution box connector), and the 4.75" hole cutter (expensive but worth it ).

I grew up in Rockville but currently live in Salisbury. You're welcome to take a listen any time.

From your detailed (thanks) advice on the adjustments, can I get some clarification on this part -
"As for the amp's crossover filters, I have the front SLC 210.25 NG (4"+1") hi-passed at 95 Hz, the rear SLC 230.25 NG (5.25"+1") hi-passed at 80 Hz, and the SWS-8X (8") lo-passed at 145 Hz. Nothing too scientific here, but it seems to work."

You are referring to the adjustments of the 3 channel outputs on the JL Audio right?
So switch to HP on Channel 1 and 2 and turn the dials to 95Hz and 80Hz respectively and LP for Channel 3 at 145Hz
BTW my front and rears are BSW and subs are SWS8s. Perhaps I should put both front and rear at 95Hz? I'd like a little more bass from the BSWs and I don't turn the volume up that much.

I, like you think the highs are a bit muted - in the sense I'm not getting the "really high" highs. I was thinking of changing to the following:
S1: B (3800)
S2: 3 (notch on)
S3: 3 (middle optimum)
S4: -8 (tweeter polarity in phase)
S5: +7 (tweeter polarity in phase)

I think I'll try changing the front passenger side first and listen to that for awhile, make sure it doesn't become fatiguing.

I don't particularly like my current rears (Infinity 4032cf 4" coaxials) except their tone seems to be close to the Rainbows and they are clean - used only for fill right now. After reading your post, I might be inclined to install a set of 5.25" Rainbow coaxials in the rear deck - but I'm still not sure I want to permanently alter the rear deck. Decisions, decisions...

My current amp settings are: fronts hi-passed at 110-120Hz, rears at 130Hz and sub at 100Hz. I'd like to make the front Rainbows work harder at low frequencies, as they have a pleasant low end which seems to work well at low listening volumes - but it falls apart when I crank it up a little more.

If you think the rears sound bad, they're too loud. Rears are for fill. Their tonality, in anything other than a 5.1 setup, is irrelvant. Also, I'll bey my ass that you have some phase issues. In 20 years of doing car audio I've never seen, built, or heard, a car without a processor with a delay, that didn't need at least one mid or midbass polarity reversed.

If you're going to add an EQ just skip and go right to a full-bore processor like a Zapco DSP-6SL or Audison Bit One if you want to do the tweaking yourself. If not, try the JBL MS-8.

If you think the rears sound bad, they're too loud. Rears are for fill. Their tonality, in anything other than a 5.1 setup, is irrelvant. Also, I'll bey my ass that you have some phase issues. In 20 years of doing car audio I've never seen, built, or heard, a car without a processor with a delay, that didn't need at least one mid or midbass polarity reversed.

If you're going to add an EQ just skip and go right to a full-bore processor like a Zapco DSP-6SL or Audison Bit One if you want to do the tweaking yourself. If not, try the JBL MS-8.

The processors seem like a good way to cure a number of problems, but my budget doesn't extend that far. Ans I've never used sophisticated audio analysis tools before, I wouldn't know what to do.

That said, do you think it would be worth paying an audio shop to do a little tweaking of my existing system?

The processors seem like a good way to cure a number of problems, but my budget doesn't extend that far. Ans I've never used sophisticated audio analysis tools before, I wouldn't know what to do.

That said, do you think it would be worth paying an audio shop to do a little tweaking of my existing system?

Possibly, but have a listen to work they've already done to make sure they can deliver what you want.

And you don't need anything but your ears for any of the processors I mentioned. Some guidance from those of us that are experienced helps as well but figuring it out for yourself is far more valuable and beneficial.

Example, the Bit One is nothing but crossovers, eq, polarity, and time delay. You've already done most of these things yourself. Don't let the technology intimidate you. The DSP-6 has a parametric eq so it's a bit more advanced and requires a bit more knowledge, but it's not bad. The MS-8 is as easy as it gets. It does everything for you! You just adjust the volume and turn your head with some headphones on. It's great.

Ok, before anyone jumps in and says to check your grounds or any other such nonsense you need to see where the problem is exactly. Wife your front speakers are fine it's probably not the amp but we're going to make sure.

First, swap front and rear RCAs. If the noise moves to the front it's the rcas or the integration adapter. If it doesn't, swap the RCAs back. And swap the front and rear speaker cables. If the noise moves it's either the amp, rear speakers, or rear speaker wires. To find out which, connect a known good speaker and see if there is noise. No noise means speaker or wire. Noise means bad amp. If there's noise with the test speaker run a new speaker wire to one rear at a time and see which makes noise. If nothing on either, it's the wire. If only on speaker, replace that speaker.

Ok, before anyone jumps in and says to check your grounds or any other such nonsense you need to see where the problem is exactly. Wife your front speakers are fine it's probably not the amp but we're going to make sure.

First, swap front and rear RCAs. If the noise moves to the front it's the rcas or the integration adapter. If it doesn't, swap the RCAs back. And swap the front and rear speaker cables. If the noise moves it's either the amp, rear speakers, or rear speaker wires. To find out which, connect a known good speaker and see if there is noise. No noise means speaker or wire. Noise means bad amp. If there's noise with the test speaker run a new speaker wire to one rear at a time and see which makes noise. If nothing on either, it's the wire. If only on speaker, replace that speaker.

When I was experimenting and I plugged the factory balanced differential signal into a component that used common ground input I got this exact effect. No whine in the front but whine in the rear speakers even though the fronts and the underseats were the only think hooked up to the amp. The rears were running of the factory hi-fi amp.

After reading the user manual for the Rainbows, they mention the optimal sound can be achieved by setting "reference soft" on the driver's side and "middle optimum" on the passenger side - to achieve non-fatiguing sound given that one side is much closer to the driver's ear.

So far so good - switching balance left to right I definitely notice the driver's side being softer and the passenger side brighter. I'll keep it this way for 1 week and if it all sounds good, I might do the same changes to the driver's side as well.

Several other observations:
- USB memory stick sounds a LOT better than iPod, even with the iPod EQ set to flat. iPod sounds lifeless by comparison. (All on the same songs, and iPod was loaded up from the same 320kbps MP3 source songs).
- There's a slight hiss when I set the key on "accessory on" position and headunit off. Doesn't bother me.
- There's a slight pop when turning the headunit on. I am a bit concerned about this one.